All prints are identified by a number, which appears in a
number block in the lower right-hand corner of the title
block. It may also be shown in other places—such as
near the top border line, in the upper right-hand corner,
or on the reverse side of the print at both ends—so that
the number will show when the print is folded or rolled.
The purpose of the number is quick identification of a
print. If a print has more than one sheet and each sheet
has the same number, this information is included in
the number block, indicating the sheet number and the
number of sheets in the series.

Reference and Dash Numbers

Reference numbers that appear in the title block refer
you to the numbers of other prints. When more than one detail is shown on a drawing, dash numbers are used.
Both parts would have the same drawing number plus
an individual number, such as 40267-1 and 40267-2.

In addition to appearing in the title block, dash numbers
may appear on the face of the drawing near the parts
they identify. Dash numbers are also used to identify
right-hand and left-hand parts.

In aircraft, many parts on the left side are like the
corresponding parts on the right side but in reverse.
The left-hand part is always shown in the drawing.
The right-hand part is called for in the title block.
Above the title block a notation is found, such as:
470204-1LH shown; 470204-2RH opposite. Both
parts carry the same number, but the part called for
is distinguished by a dash number. Some prints have
odd numbers for left-hand parts and even numbers for
right-hand parts.

Universal Numbering System

The universal numbering system provides a means of
identifying standard drawing sizes. In the universal
numbering system, each drawing number consists of
six or seven digits. The first digit is always 1, 2, 4, or
5, and indicates the size of the drawing. The remaining
digits identify the drawing. Many firms have modified
this basic system to conform to their particular
needs. Letters may be used instead of numbers. The
letter or number depicting the standard drawing size
may be prefixed to the number, separated from it by
a dash. Other numbering systems provide a separate
box preceding the drawing number for the drawing
size identifier. In another modification of this system,
the part number of the depicted assembly is assigned
as the drawing number.